Eruptions of the Yellowstone volcanic system have included the two largest volcanic eruptions in North America in the past few million years; the third largest was at Long Valley in California and produced the Bishop ash bed.
On the diesel Passat, the TDI badge stands for Turbocharged Direct Injection, which isn't really all that helpful as the gasoline-powered Passat is also turbocharged and also uses direct injection. Volkswagen attempts to clear this up by calling this Passat the Passat TDI Clean Diesel.
That same engine in the Passat TDI was fitted with Selective Catalytic Reduction (SCR), also known as urea aftertreatment, starting in 2012. Finally, a new generation of 2.0-liter diesel engine, known as EA288, is fitted to various VW vehicles (the Golf TDI, for instance) starting with the 2015 model year.